What are ADSL VCI/VPI and what to use ?
A DSL modem needs to have the Virtual Path Identifier (VPI) and Virtual Circuit Identifier (VCI) set in order to work correctly. In essence, these two numbers tell the DSL equipment on both ends that they should talk to each other, you can think of them as having a similar functionality to dialing a number on a regular phone line. Each DSL provider uses a set of these two numbers.
Bellow is the actual technical definition of both:
VPI (Virtual Path Identifier) is an eight-bit field in an ATM cell's header that identifies the virtual path (a bundle of virtual channels that have the same endpoint) to which the cell belongs as it travels through an ATM network.
VCI (Virtual Channel Identifier) is a 16-bit field in an ATM cell's header that identifies the cell's next destination as it travels through an ATM network (similar to Frame Relay's DLCI). A virtual channel is a logical connection between two end devices on an ATM network.
An ATM switch uses either the VPI, VCI, or a combination of both to route the cell to its destination.
For a list of known VCI/VPI values, please see this article.
Please note that some ISP's (Earthlink, Mindspring, Speakeasy, etc.) may use your local telco for the network services. In such cases, just use the VPI/VCI values for your telco/CLEC.